JPH05243950A - Drive circuit of switching element - Google Patents

Abstract

PURPOSE:To obtain a switching element driving circuit which does not generate a noise accompanied with electromagnetic connection and can operate at high speed by connecting a transistor between the output terminals of a direct voltage source and setting it on/off through a photo-coupler. CONSTITUTION:When a solar battery SB is irradiated with a lamp LP, a capacitor C is charged and when the side of the phototransistor of the photocoupler PC is in an off state in the state where a charging voltage satisfactorily becomes high, a transistor Q1 becomes off and a transistor Q2 becomes on. Current flowing through the transistor Q2 quickly charges inter-electrode capacitance to set FET into an on state. At the time of finishing charging. The transistor Q2 comes into a nearly off state. Thereafter, when a high voltage is supplied to the side of the photo diode of the photo-coupler PC to make it emit light, the side of the photo-transistor Q1 is conducted to set the transistor Q1 in an on state and transistor Q2 completely in an off state. Then, the charge of FET is quickly discharged through Q1 and FET comes into the off state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching element drive circuit used for driving a switching element or the like which constitutes an H-bridge circuit for driving a motor.

[0002]

2. Description of the Related Art In an electric vehicle, the terminal voltage is 100 to 2
A DC battery or an AC motor is driven by a storage battery of about 00 volt. When an AC motor is used as the motor, of course, even a DC motor without a brush requires a motor drive circuit having a function of inverting the voltage supplied to the motor. As such a motor drive circuit, an H bridge circuit as shown in FIG. 6 is used.

In this H-bridge circuit, four switching elements S1 to S4, each of which is a high-power FET, are connected in series in parallel between power supply lines B1 and B2 connected to a storage battery BT, and also switching elements S1 and S4. And the connection points of the switching elements S2 and S3 are connected to the input terminals of the motor (M), respectively. Each of the switching elements S1 to S4 is driven by an individual drive circuit D1 to D4. When the switching elements S1 and S2 are on and the switching elements S3 and S4 are off, a voltage of a predetermined polarity is supplied to the motor M, and conversely, the switching elements S and S2 are off and the switching element S3 is on.
When S4 is in the ON state, a voltage of opposite polarity is supplied to the motor M.

Among the drive circuits D1 to D4 in FIG. 6, especially the drive circuits D1 and D3 on the high voltage side have a large potential difference from the vehicle body or the like which is kept at the ground potential, so that careful insulation and measures against noise should be taken. Will be needed. A typical combination of the drive circuits D1 to D4 is a combination of a DC-DC down converter, a transistor and a photo coupler. This is represented by the drive circuit D1 as shown in FIG.
Two transistors Q1 and Q2 are connected in series between the output terminals of the DC-DC down converter DCV, and one transistor is turned on / off by the photocoupler PC, so that the two transistors Q1 and Q2 are turned on / off alternately. It is configured to turn off and supply a drive signal to the switching element S1 from the connection point of each transistor.

As the drive circuit, in addition to the drive circuit shown in FIG. 7, there is also a configuration in which a pulse transformer is used and its secondary output terminal is connected to the gate terminal and the source terminal of the switching element S1. Alternatively, as disclosed in U.S. Pat. No. 4,227,098, a large number of photodiodes are connected in series between the gate terminal and the drain terminal of the FET, which is a switching element, and the light emitting element is connected to this photodiode array. There is also known a configuration in which the FET is turned on / off by a voltage generated by irradiating the light.

[0006]

The conventional drive circuit shown in FIG. 7 has a problem that the manufacturing cost is high because the number of parts of the DC-DC down converter is large. Also, D
There is also a problem that noise due to electromagnetic coupling easily occurs in the C-DC down converter.

The above-mentioned conventional drive circuit using a pulse transformer has a problem that it is difficult to operate at low speed and electromagnetic noise is easily generated.

The drive circuit disclosed in the above US patent includes
Since a high impedance FET is connected to an array in which a large number of photodiodes are connected in series, there is a problem that the rising and falling speeds are limited.

[0009]

A drive circuit for a switching element according to the present invention comprises a photocoupler in which a transistor is connected between output terminals of a DC power supply which is provided with a photoelectric conversion circuit which receives a light beam and generates a DC power supply voltage. The transistor is configured to supply a drive signal to the switching element by turning on / off this transistor.

[0010]

In the drive circuit of the present invention, since the bias voltage of the transistor is generated by irradiating the photoelectric conversion circuit with a light beam, the noise due to the electromagnetic coupling is different from the case where the DC-DC down converter or the pulse transformer is used. Does not occur. Further, since the photocoupler capable of high speed operation is used in the signal path, high speed driving becomes possible unlike the case of the above-mentioned US patent.

[0011]

1 is a circuit diagram showing the structure of a switching element drive circuit according to an embodiment of the present invention, together with the switching element to be driven. In this drive circuit, a solar cell SB is connected to transistors Q1 and Q2 connected in series via a diode d and a capacitor C, and a resistor R1 is connected.
And the phototransistor side of the photocoupler PC to bias the base terminals of the transistors Q1 and Q2, and drive voltage from the connection point of the transistors Q1 and Q2 to the gate terminal of the FET that constitutes the switching element via the resistor R2. Is configured to supply. The emitter terminal of the transistor Q1 is the switching element S1.
Is connected to the source terminal of.

When the lamp L is turned on to illuminate the solar cell SB, the generated photovoltaic charges the capacitor C through the diode d and starts supplying the bias voltage to the transistors Q1 and Q2. If the phototransistor side of the photocoupler PC is off with the charging voltage of the capacitor C sufficiently high, the transistor Q1 will be off as the base voltage increases.
On the contrary, the transistor Q2 is turned on as the base voltage thereof rises. The current flowing through the transistor Q2 rapidly charges the capacitance between the gate electrode and the source and drain electrodes of the FET through the resistor R2, and quickly turns on the FET. When charging of the inter-electrode capacitance of the FET is completed, the current flowing through the transistor Q2 becomes extremely small and the transistor Q2 is almost turned off.

After that, when a high voltage is supplied to the photodiode side of the photocoupler PC through the inverter I to cause light emission, the phototransistor side becomes conductive, the base voltage of the transistor Q1 drops, and the transistor Q1 turns on. At the same time, the transistor Q2 is completely turned off. Along with this, the electric charge accumulated in the inter-electrode capacitance of the TET is rapidly discharged through the transistor Q1, and the FET is quickly turned off. When this discharge ends, the current flowing through the transistor Q1 becomes extremely small, and the transistor Q1 is almost turned off.

As described above, since the current flowing through the transistor Q1 is small enough to charge the inter-electrode capacitance of the FET, the power consumption of this drive circuit is small. As a result, a high-quality bias that does not include noise associated with electromagnetic coupling can be achieved with a simple structure in which a solar cell and a lamp are combined. Further, since the transistors Q1 and Q2 are turned on / off via the photocoupler PC, high speed operation is possible.

When the drive circuit of FIG. 1 is used as the drive circuits D1 to D4 of the H-bridge circuit shown in FIG. 6, the four systems of solar cells are SB1 to SB4 in the circuit of FIG.
As shown by, it is configured to receive light irradiation from a common lamp L.

The physical structure of the circuit of FIG. 2 is, for example, as shown in FIG. 3, a solar cell SB on a printed wiring board PB.
1 to SB4 are arranged, surrounded by a shielding box BX, and a lamp LP is attached to the upper part of the shielding box.

FIG. 4 shows a solar cell SB from a lamp (not shown) at a remote place via optical fibers F1 to F4.
An example of a structure for irradiating 1 to SB4 is shown.

FIG. 5 shows the lamp LP1 in the shielding box of FIG.
LP2 is added to guide natural light outside the vehicle collected using a lens or the like to the solar cells SB1 to SB4 through the optical fibers F1 to F4 in fine weather and to use the solar cell S in cloudy weather.
A configuration example in which the power consumption of the lamps is further effectively reduced by detecting that the electromotive forces of B1 to SB4 have decreased and automatically turning on the lamps LP1 and LP2 will be shown.

Above, the solar cell and the transistors Q1 and Q2
Although the configuration in which the capacitor is connected between the above and the above is illustrated, a configuration in which a secondary storage battery is connected instead of this capacitor may be adopted.

Further, a configuration has been shown in which two transistors are connected in series between a DC power source by a solar cell and turned on / off alternately, but if it is not necessary to save power consumption, this on / off Alternatively, the load resistance and one transistor may be used.

[0021]

As described above in detail, since the drive circuit of the present invention is configured to irradiate the photoelectric conversion circuit with light rays to generate the bias voltage of the transistor, the DC-D
Unlike the case of using a C down converter or pulse transformer, noise due to electromagnetic coupling does not occur, and a high-speed operation is possible because a photocoupler capable of high-speed operation is used in the signal path. The effect is produced.

In particular, if the transistors Q1 and Q2 shown in the embodiment of FIG. 1 are alternately turned on / off, the power consumption of the drive circuit can be made extremely small, so that the power consumption of the lamp LP is greatly increased. Savings can be achieved and the effects of the present invention can be further enhanced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a switching element drive circuit according to an embodiment of the present invention together with a switching element to be driven.

FIG. 2 is a circuit diagram showing a configuration of a power supply unit when the switching circuit of FIG. 1 is applied to an H bridge circuit.

3 is a cross-sectional view showing an example of a physical structure of the circuit of FIG.

4 is a cross-sectional view showing another example of the physical structure of the circuit of FIG.

5 is a cross-sectional view showing still another example of the physical structure of the circuit of FIG.

FIG. 6 is a circuit diagram showing an example of a configuration of a motor drive circuit using an H bridge circuit, which is one of application examples of the present invention.

FIG. 7 is a circuit diagram showing a typical example of a conventional drive circuit.

[Explanation of reference signs] Q1, Q2 transistor SB Solar cell (photoelectric conversion circuit) LP lamp PC Photocoupler FET Field-effect transistor (switching element) to be driven

Claims (3)

[Claims] 1. A drive circuit for a switching element, wherein at least one transistor is connected between output terminals of a DC power supply, and a drive signal is supplied to the switching element by turning on / off the at least one transistor. The DC power supply includes a photoelectric conversion circuit that receives a light beam and generates a DC power supply voltage, and the transistor is turned on / off via a photocoupler. 2. The switching element according to claim 1, wherein the switching element is a field effect transistor, and the transistor connected between the output terminals of the DC power supply is composed of two transistors connected in series, and one of the transistors is the photo transistor. ON / via coupler
A switching element drive circuit, in which each transistor is alternately turned on / off when turned off. 3. The switching element drive circuit according to claim 2, wherein the switching element is a switching element forming an H bridge circuit for driving a motor.